Casey Stoner said illness was the main factor in his inability to keep up with the Yamahas in the Catalunya Grand Prix.
The Ducati rider held on to third by fending off Honda's Andrea Dovizioso, but gradually lost touch with the dominant Valentino Rossi and Jorge Lorenzo during the race.
Although Stoner had been struggling to get his Ducati onto the Yamahas' pace during practice and qualifying, he felt the bike was much better in the race. But by then he had begun to lose strength due to his deteriorating health, as a flu condition had worsened by race day.
"I'm quite disappointed because on Friday everything started off pretty well," said Stoner. "We had a small crash but the bike felt good.
"Then on Saturday we really struggled with the bike. It was way too far off the pace to even be competitive. For the race we changed a few things and made a big improvement and the bike was there.
"But I've been slowly getting a little more sick each day and after the warm-up this morning I was cramping and having all sorts of problems, and that was after a cool warm-up with not too many laps.
"I was really afraid of not finishing this race, and we did everything we could to prepare for it. But halfway through I gave up. I was absolutely dead and had nothing left, so decided just to try and run around to get points.
"I managed to keep braking late to keep Andrea behind me, and on the last two laps I put a bit more effort in."
He is optimistic that he would have been a victory contender had he been in better health.
"Hopefully we'll be fitter and stronger by Assen," Stoner said. "With the solution we found today, I think we were maybe capable of staying with them if I was riding at 100 per cent."